1. Field of the Invention
The present invention relates to a semiconductor laser device. More particularly, the invention relates to a structure of a protective film provided on a light emitting surface of a semiconductor laser device, a production method therefor, and a jig for use in the production method.
2. Description of the Related Art
Known as the prior art related to the present invention is a semiconductor laser device which has a protective film covering only a part of a light emitting surface including at least an active layer region but not entirely covering the light emitting surface.
Since the protective film covers only the part of the light emitting surface of the semiconductor laser device, a stress occurring in the protective film is reduced as compared with a case where the protective film entirely covers the light emitting surface. This reduces a damage to the active layer and prevents delamination of the protective film (see, for example, Japanese Unexamined Patent Publication No. 8-97496 (1996)).
The light emitting surface of the semiconductor laser device is liable to be oxidized by a laser beam emitted from the semiconductor laser device per se. The oxidation of the light emitting surface tends to adversely affect the reliability and service life of the semiconductor laser device.
For prevention of the oxidation of the light emitting surface, an oxide film such as of Al2O3 is formed as the protective film on the light emitting surface by vacuum vapor deposition.
In the formation of the Al2O3 protective film by the vapor deposition, however, the partial pressure of oxygen molecules generated by decomposition of the oxide material for the protective film is increased immediately after the start of the vapor deposition. The oxygen molecules generated by the decomposition during the vapor deposition impinge on the light emitting surface or are combined with the light emitting surface, thereby damaging the light emitting surface. Particularly, where the active layer of the semiconductor laser device and its peripheral layer contain aluminum, the damage is further exacerbated.
Therefore, it is a general practice to form an Si thin film on the light emitting surface by vapor deposition before the formation of the oxide protective film. The formation of the Si thin film has no possibility of generating oxygen due to the decomposition of the material in the vapor deposition.
Meanwhile, the semiconductor laser device includes a pair of gold electrodes provided on its front and back faces. In general, the front electrode is patterned into an asymmetric contour for discrimination between a major light emitting surface side and a rear side of the semiconductor laser device. On the other hand, the back electrode is generally provided on the entire back face of the semiconductor laser device in consideration of the labor and costs associated with the patterning.
In this case, an edge of the back electrode is exposed to the light emitting surface, so that the aforesaid Si thin film contacts the edge of the back electrode. With the Si thin film in contact with the back electrode, gold as the electrode material is diffused into the Si thin film by heat applied for the formation of the protective film by the vapor deposition. If gold is diffused into the Si thin film to reach the active layer region serving as a light emitting point of the semiconductor laser device, the maximum output of the semiconductor laser device is reduced to lower than half as compared with a case where the Si thin film is free from the diffusion of gold. This significantly reduces the reliability of the semiconductor laser device.
The diffusion of gold can be prevented, if the protective film is provided as partly covering the light emitting surface so as not to contact the edge of the back electrode. However, a protective film formation area limited to a part of the light emitting surface makes it difficult to sufficiently protect the light emitting surface.